KR20130027012A - Semiconductor device and driving method thereof - Google Patents

Abstract

The semiconductor device includes a photodiode, a first transistor, a second transistor, and a third transistor. The second transistor and the third transistor have a function of holding charge accumulated in the gate of the first transistor. In the period in which the second transistor and the third transistor are turned off, the voltage level of the voltage applied to the gate of the second transistor is set lower than the voltage level of the source of the second transistor and the voltage level of the drain of the second transistor. The voltage level of the voltage applied to the gate of the three transistors is set lower than the voltage level of the source of the third transistor and the voltage level of the drain of the third transistor.

Description

Semiconductor device and driving method therefor {SEMICONDUCTOR DEVICE AND DRIVING METHOD THEREOF}

The technical field relates to a photosensor and a driving method thereof. The technical field also relates to a display device including a photosensor and a driving method thereof. In addition, the technical field relates to a semiconductor device including a photosensor and a driving method thereof.

Recently, a display device equipped with a light detection sensor (also called a "photo sensor") has attracted attention. In the display device including the photosensor, the display screen also serves as an input area. A display device having an image capture function is one example of such a display device. (See, for example, Patent Document 1).

Examples of semiconductor devices equipped with photosensors include CCD image sensors and CMOS image sensors. Such image sensors are used in electronic devices such as digital still cameras and mobile phones, for example.

In a display device equipped with a photosensor, light is first emitted from the display device. When light is input into the area where the object to be detected exists, the light is blocked by the object to be detected and partially reflected. Light reflected by the object to be detected is detected by a photosensor in a pixel of the display device, whereby the object to be detected can be found in the area.

In a semiconductor device including a photosensor, the light emitted from the object to be detected or the external light reflected by the object to be detected is detected directly by the photosensor or collected by an optical lens or the like and then detected.

Japanese Patent Application Publication No. 2001-292276

In a semiconductor device including a photosensor, each pixel is provided with a circuit including a transistor in order to collect electrical signals generated by light detection of the photosensor mounted on each pixel.

However, it is difficult to accurately convert incident light into an electrical signal because of variations in electrical characteristics such as threshold voltages of transistors provided in each pixel.

An object of one embodiment of the present invention is to provide a semiconductor device comprising a photosensor capable of accurately converting incident light into an electrical signal.

An embodiment of the present invention is a semiconductor device including a photodiode, a first transistor, a second transistor, a third transistor, and a fourth transistor. The photodiode has a function of supplying a charge corresponding to incident light to the gate of the first transistor through the second transistor. The first transistor has a function of accumulating the electric charge supplied to the gate and converting the accumulated electric charge into an output signal. The second transistor has a function of holding charge accumulated in the gate of the first transistor. The third transistor has a function of discharging the charge accumulated in the gate of the first transistor and a function of maintaining the charge accumulated in the gate of the first transistor. The fourth transistor has a function of controlling the reading of the output signal. In the period in which the second transistor and the third transistor are turned off, the voltage level of the voltage applied to the gate of the second transistor is lower than the voltage level of the source of the second transistor and the voltage level of the drain of the second transistor. The voltage level of the voltage applied to the gate of is lower than the voltage level of the source of the third transistor and the voltage level of the drain of the third transistor.

Another embodiment of the present invention is a semiconductor device including a photodiode, a first transistor, a second transistor, a third transistor, and a fourth transistor. The photodiode has a function of supplying a charge corresponding to incident light to the gate of the first transistor through the second transistor. The first transistor has a function of accumulating the electric charge supplied to the gate and converting the accumulated electric charge into an output signal. The second transistor has a function of holding charge accumulated in the gate of the first transistor. The third transistor has a function of discharging the charge accumulated in the gate of the first transistor. The fourth transistor has a function of controlling the reading of the output signal. In the period in which the second transistor and the third transistor are turned off, the voltage level of the voltage applied to the gate of the second transistor is lower than the voltage level of the wiring electrically connected to the photodiode, and the voltage applied to the gate of the third transistor. The voltage level of is lower than the voltage level of the photosensor reference signal line.

Another embodiment of the present invention is a semiconductor device including a photodiode, a first transistor, a second transistor, a third transistor, and a fourth transistor. The photodiode has a function of supplying a charge corresponding to incident light to the gate of the first transistor through the second transistor. The first transistor has a function of accumulating the electric charge supplied to the gate and converting the accumulated electric charge into an output signal. The second transistor has a function of holding charge accumulated in the gate of the first transistor. The third transistor has a function of discharging the charge accumulated in the gate of the first transistor and a function of maintaining the charge accumulated in the gate of the first transistor. The fourth transistor has a function of controlling the reading of the output signal. The semiconductor layer of the second transistor and the semiconductor layer of the third transistor, which are electrically connected to the gate of the first transistor, include an oxide semiconductor. In the period in which the second transistor and the third transistor are off, the voltage level of the voltage applied to the gate of the second transistor is lower than the voltage level on the low voltage side of the source and drain of the second transistor, and is applied to the gate of the third transistor. The voltage level of the given voltage is lower than the voltage level on the low voltage side of the source and the drain of the third transistor.

Another embodiment of the present invention is a semiconductor device including a photodiode, a first transistor, a second transistor, a third transistor, and a fourth transistor. The photodiode has a function of supplying a charge corresponding to incident light to the gate of the first transistor through the second transistor. The first transistor has a function of accumulating the electric charge supplied to the gate and converting the accumulated electric charge into an output signal. The second transistor has a function of holding charge accumulated in the gate of the first transistor. The third transistor has a function of discharging the charge accumulated in the gate of the first transistor. The fourth transistor has a function of controlling the reading of the output signal. The semiconductor layer of the second transistor and the semiconductor layer of the third transistor, which are electrically connected to the gate of the first transistor, include an oxide semiconductor. In the period in which the second transistor and the third transistor are turned off, the voltage level of the voltage applied to the gate of the second transistor is lower than the voltage level of the wiring electrically connected to the photodiode, and the voltage applied to the gate of the third transistor. The voltage level of is lower than the voltage level of the photosensor reference signal line.

It should be noted that a semiconductor device represents a device having semiconductor properties, and all entities having such a device. For example, a display device having a transistor is simply referred to as a semiconductor device in some cases.

A semiconductor device including a photosensor capable of accurately converting incident light into an electrical signal can be provided.

In addition, since the accumulation operation is performed simultaneously in the plurality of photosensors, the accumulation operation can be completed in a short time, so that an image of the to-be-detected object without distortion can be obtained even when the object moves quickly.

In addition, the transistor controlling the accumulation operation has an extremely low off current because it includes an oxide semiconductor. Thus, the incident light can be accurately converted into an electrical signal even though the number of photosensors increases and the selection operation requires a longer time. Therefore, a high resolution image can be obtained.

1 is a diagram illustrating an example of a display device according to an embodiment of the present invention.
2 illustrates an example of a display device according to an embodiment of the present invention.
3 is a timing chart according to an embodiment of the present invention.
4 is a timing chart according to an embodiment of the present invention.
5 is a timing chart according to an embodiment of the present invention.
6A to 6C are circuit diagrams showing an example of a photosensor according to one embodiment of the present invention.
7 is a diagram illustrating an example of a semiconductor device according to one embodiment of the present invention.
8 is a graph showing electrical characteristics of transistors.
9 is a diagram showing an example of a semiconductor device according to one embodiment of the present invention.
10 is a timing chart according to an embodiment of the present invention.

Embodiments will be described in detail below with reference to the drawings. The following embodiments can be implemented in a variety of modes, and mode and details can be modified in various ways without departing from the spirit and scope of the invention to those skilled in the art It should be noted that it is obvious. Accordingly, the present invention should not be construed as limited to the description of the embodiments. It should be noted that in all the drawings for describing the embodiments, the same parts or parts having similar functions are denoted by the same reference numerals and the description thereof is omitted.

(Embodiment 1)

In this embodiment, the structure of the display device, which is a semiconductor device including a photosensor, and its operation will be described with reference to FIGS. 1, 2, and 3. It should be noted that the display device including the photosensor may be used as an optical touch sensor.

The structure of the display device will be described with reference to FIG. 1. The display panel 100 includes a pixel circuit 101, a display element control circuit 102, and a photosensor control circuit 103.

The pixel circuit 101 includes a plurality of pixels 104 arranged in a matrix in row and column directions. Each pixel 104 includes a display element 105 and a photosensor 106. The photosensor need not be provided for each pixel 104 but may be provided for every two or more pixels 104. Alternatively, the photosensor may be provided outside the pixel 104.

The circuit diagram of the pixel 104 will be described with reference to FIG. 2. The pixel 104 includes a display element 105 having a transistor 201 (also called a pixel transistor), a storage capacitor element 202, and a liquid crystal element 203; And a photodiode 204, a transistor 205 (also referred to as a first transistor), a transistor 206 (also referred to as a second transistor), a transistor 207 (also referred to as a third transistor), and a transistor 208 which are light receiving elements. Photoelectric sensor 106 (also referred to as a fourth transistor).

In the display element 105, the gate of the transistor 201 is connected to the gate signal line 209, one of the source and the drain of the transistor 201 is connected to the video data signal line 210, and the other of the source and the drain. Is connected to one electrode of the storage capacitor element 202 and one electrode of the liquid crystal element 203. The other electrode of the storage capacitor 202 and the other electrode of the liquid crystal element 203 are each maintained at a constant voltage level. The liquid crystal element 203 is an element including a pair of electrodes and a liquid crystal layer between the pair of electrodes.

In the case of an explicit statement that "is connected to A and B," A and B are electrically connected, A and B are functionally connected, and A and B are directly connected. Note that it includes.

The transistor 201 has a function of controlling the injection or discharge of charge to or from the storage capacitor 202. For example, when a high-level voltage is applied to the gate signal line 209, the voltage at the voltage level of the video data signal line 210 is applied to the storage capacitor element 202 and the liquid crystal element 203. The storage capacitor 202 has a function of holding a charge corresponding to the voltage applied to the liquid crystal element 203. The contrast (gradation) of light passing through the liquid crystal element 203 is made by using a change in the polarization direction due to the application of voltage to the liquid crystal element 203, whereby image display is realized. As the light passing through the liquid crystal element 203, light emitted from the light source (backlight) on the back of the display device is used.

In the transistor 201, an amorphous semiconductor, a microcrystalline semiconductor, a polycrystalline semiconductor, an oxide semiconductor, a single crystal semiconductor, or the like can be used. In particular, display quality can be increased by obtaining transistors of very low off current using oxide semiconductors.

Although the display element 105 described herein includes a liquid crystal element, the display element 105 may include other elements such as a light emitting element. The light emitting element is an element whose luminance is controlled by a current or a voltage, and specific examples thereof are a light emitting diode and an organic light emitting diode (OLED). In the present embodiment, the display element 105 and the photosensor 106 are described as being provided in the structure of the optical touch sensor (also called an optical touch panel), but a structure in which the display element is removed may also be used. In this case, an image sensor provided with a plurality of photosensors can be obtained.

In the photosensor 106, one electrode of the photodiode 204 is connected to a wiring 211 (also called a ground line), and the other electrode thereof is connected to one of a source and a drain of the transistor 206. One of the source and the drain of the transistor 205 is connected to the photosensor reference signal line 212, and the other of the source and the drain is connected to one of the source and the drain of the transistor 208. The gate of the transistor 206 is connected to the gate signal line 213, and the other of the source and the drain of the transistor 206 is connected to the gate of the transistor 205 and one of the source and the drain of the transistor 207. The gate of the transistor 207 is connected to the photodiode reset signal line 214, and the other of the source and the drain of the transistor 207 is connected to the photosensor reference signal line 212. The gate of the transistor 208 is connected to the gate signal line 215, and the other of the source and the drain of the transistor 208 is connected to the photosensor output signal line 216.

In the photodiode 204, an amorphous semiconductor, a microcrystalline semiconductor, a polycrystalline semiconductor, an oxide semiconductor, a single crystal semiconductor, or the like can be used. In particular, in order to improve the ratio (quantum efficiency) of the electrical signal generated from the incident light, it is preferable to use a single crystal semiconductor (for example, single crystal silicon) having few crystal defects. As the semiconductor material, it is preferable to use a silicon semiconductor such as silicon or silicon germanium in which crystallinity can be easily improved.

In the transistor 205, an amorphous semiconductor, a microcrystalline semiconductor, a polycrystalline semiconductor, an oxide semiconductor, a single crystal semiconductor, or the like can be used. In particular, the transistor 205 has a function of accumulating the charge supplied from the photodiode 204 through the transistor 206 at a node connected to the gate and converting the accumulated charge into an output signal. Thus, single crystal semiconductors are preferably used to obtain transistors with high mobility. As the semiconductor material, it is preferable to use a silicon semiconductor such as silicon or silicon germanium in which crystallinity can be easily improved.

In the transistor 206, an amorphous semiconductor, a microcrystalline semiconductor, a polycrystalline semiconductor, an oxide semiconductor, a single crystal semiconductor, or the like can be used. In particular, the transistor 206 has a function of maintaining the charge of the gate of the transistor 205 by controlling the on / off of the transistor 206. Thus, the transistor 206 preferably uses an oxide semiconductor to have a very low off current.

In the transistor 207, an amorphous semiconductor, a microcrystalline semiconductor, a polycrystalline semiconductor, an oxide semiconductor, a single crystal semiconductor, or the like can be used. In particular, the transistor 207 has a function of discharging the charge of the gate of the transistor 205 and controlling the charge of the gate of the transistor 205 by controlling the on / off of the transistor 207. Thus, the transistor 207 preferably uses an oxide semiconductor to have a very low off current.

In the transistor 208, an amorphous semiconductor, a microcrystalline semiconductor, a polycrystalline semiconductor, an oxide semiconductor, a single crystal semiconductor, or the like can be used. In particular, the single crystal semiconductor is preferably used in the transistor 208 such that the transistor 208 has a high mobility and has a function of supplying the output signal of the transistor 205 to the photosensor output signal line 216. As the semiconductor material, it is preferable to use a silicon semiconductor such as silicon or silicon germanium in which crystallinity can be easily improved.

The display element control circuit 102 is a circuit for controlling the display element 105, and the signal is input to the display element 105 via a signal line (also called a source signal line) such as a video data signal line. ); And a display element driving circuit 108 in which a signal is input to the display element 105 via a scan line (also called a gate signal line). For example, the display element driving circuit 108 on the scan line side has a function of selecting display elements included in pixels in a specific row. The display element driving circuit 107 on the signal line side has a function of supplying a voltage of a predetermined level to the display elements included in the pixels in the selected row. In the display element 105 connected to the gate signal line to which the high-level voltage is applied from the display element drive circuit 108 on the scan line side, the transistor is turned on and video data from the display element drive circuit 107 on the signal line side. Note that a voltage of the same level as that applied to the signal line is applied.

The photosensor control circuit 103 is a circuit for controlling the photosensor 106, the photosensor reading circuit 109 of the signal line side wherein the signal lines include photosensor output signal lines or photosensor reference signal lines; And a photosensor driving circuit 110 on the scan line side.

The photosensor driving circuit 110 has a function of performing the reset operation, the accumulation operation and the selection operation described below with respect to the photosensor 106 included in the pixels in a specific row.

The photosensor reading circuit 109 has a function of extracting an output signal of the photosensor 106 included in the pixels of the selected row. It should be noted that from the photosensor reading circuit 109, the output of the photosensor 106, which is an analog signal, is extracted as it is outside of the display panel using the OP amplifier. Alternatively, the output of the photosensor 106 is converted into a digital signal using an A / D conversion circuit and then extracted to the outside of the display panel.

The precharge circuit included in the photosensor reading circuit 109 will be described with reference to FIG. In FIG. 2, the precharge circuit 200 for one column of pixels includes a transistor 217 and a precharge signal line 218. It should be noted that the photosensor reading circuit 109 may include an OP amplifier or A / D conversion circuit connected to the rear end of the precharge circuit 200.

In the precharge circuit 200, before the operation of the photosensor in the pixel, the voltage level of the photosensor output signal line is set to the reference voltage level. In FIG. 2, the precharge signal line 218 is set at an H level (hereinafter, abbreviated to "H") so that the transistor 217 is turned on, so that the voltage level of the photosensor output signal line 216 is a reference voltage level (here , Low voltage level). It should be noted that it is effective to provide the storage capacitor element in the photosensor output signal line 216 so that the voltage level of the photosensor output signal line 216 is stabilized. Note that the reference voltage level can be set to a high voltage level. In that case, the conductivity type of the transistor 217 is made to be reverse polarity from the conductivity type in FIG. 2 and the precharge signal line 218 is set to an L level (hereinafter abbreviated as "L"), so that the photosensor output signal line The voltage level of 216 may be set to a reference voltage level.

It should be noted that in this embodiment, the voltage at the H-level and the voltage at the L level correspond to voltages based on high power voltage levels and voltages based on low power supply voltage levels, respectively. That is, the voltage at the H-level is a constant voltage of 3 V to 20 V, and the voltage at the L-level is a constant voltage of 0 V (also referred to as a reference voltage level or ground voltage level).

Next, the operation of the photosensor 106 will be described with reference to the timing chart of FIG. In FIG. 3, the signal 301, the signal 302, and the signal 303 correspond to voltage levels of the gate signal line 213, the reset signal line 214, and the gate signal line 215 in FIG. 2, respectively. In addition, each of the signals 304A-304C corresponds to the voltage level of the gate of the transistor 205 (voltage level of the node 219 in FIG. 2). The signal 304A shows that the light intensity incident on the photodiode 204 is high (hereinafter, high illuminance), and the signal 304B shows that the light intensity incident on the photodiode 204 is medium (hereinafter, Medium illuminance), the signal 304C shows that the illuminance of the light incident on the photodiode 204 is low (hereinafter, low illuminance). In addition, the signals 305A to 305C correspond to voltage levels of the photosensor output signal line 216, respectively, and the signals 305A to 305C show high illumination, medium illumination and low illumination, respectively.

In the period A, the voltage level of the gate signal line 213 (signal 301) is set to " H ", and the voltage level of the reset signal line 214 (signal 302) to a level lower than 0 V (hereinafter, " L2 "). The voltage level (signal 303) of the gate signal line 215 is set to " L ". Next, in the period B, the voltage level of the gate signal line 213 (signal 301) is set to "H", the voltage level of the reset signal line 214 (signal 302) is set to "H" level, and the gate signal line ( The voltage level (signal 303) of 215 is set to "L". As a result, the photodiode 204 and the transistor 206 are turned on, and the voltage level (signals 304A to 304C) of the node 219 becomes "H". At this point, a reverse bias is applied to the photodiode 204. When the voltage level of the precharge signal line 218 is set to the H level, the voltage level (signals 305A to 305C) of the photosensor output signal line 216 is precharged to "L". As described above, the periods A and B are reset operation periods.

In the present specification, a level lower than 0 V is specifically, the voltage level of the source of the transistor 206, the voltage level of the drain of the transistor 206, the voltage level of the source of the transistor 207 and the drain of the transistor 207. Note that it means a voltage level lower than the voltage level of. In this embodiment, the voltage level on the low voltage side of the source and drain of the transistors 206 and 207 is 0 V, which is the voltage level of the ground line, and the voltage level of the gate signal line 213 and the reset signal line 214 for a predetermined period. Can be said to be a level lower than 0V. That is, the voltage level on the low voltage side of the source and drain of the transistor 206 and the voltage level on the low voltage side of the source and drain of the transistor 207 are based on the circuit configuration shown in FIG. 2, respectively. The voltage level of the wiring 211 connected to the voltage sensor and the voltage level of the photosensor reference signal line 212.

Next, in the period C, the voltage level (signal 301) of the gate signal line 213 is set to "H", and the voltage level (signal 302) of the reset signal line 214 is set to "L2", The voltage level (signal 303) of the gate signal line 215 is set to "L". As a result, the voltage level (signals 304A-304C) of node 219 begins to decrease due to the current (hereinafter referred to as photocurrent) by light irradiation to photodiode 204. In the photodiode 204, the photocurrent increases due to the increase in the incident light amount; Therefore, the voltage level (signals 304A to 304C) of the node 219 changes depending on the amount of incident light. In particular, since the photocurrent greatly increases in the signal 304A having a large amount of incident light, the signal 304A, which is the voltage level of the node 219, greatly decreases in the period C. Since the photocurrent hardly flows in the signal 304C having a small amount of incident light, the signal 304C, which is the voltage level of the node 219, hardly changes in the period C. Further, in the signal 304B having a medium incident light amount, since the amount of the photocurrent increases to an intermediate amount between the amount of the signal 304A and the amount of the signal 304C, the signal 304B which is the voltage level of the node 219. The amount of decreases to an intermediate amount between the reduced amount of signal 304A and the reduced amount of signal 304C. That is, the photodiode 204 has a function of supplying a charge corresponding to incident light to the gate of the transistor 205 through the transistor 206. As a result, the channel resistance between the source and the drain of the transistor 205 changes. As described above, the period C is an accumulation operation period.

Next, in the period D, the voltage level (signal 301) of the gate signal line 213 is set to "L2", and the voltage level (signal 302) of the reset signal line 214 is set to "L2", The voltage level (signal 303) of the gate signal line 215 is set to "L". The signals 304A-304C, which are the voltage levels at node 219, are constant. Here, the voltage level of the signals 304A to 304C in the period D is determined by the amount of photocurrent of the photodiode 204 in the accumulation operation period (period C). That is, the amount of charge accumulated at the node 219 varies depending on the light incident on the photodiode 204. Oxide semiconductors are used in the semiconductor layer of the transistor 206 and the semiconductor layer of the transistor 207 to obtain transistors of very low off current, so that the accumulated charge can be sustained until subsequent selection operations are performed. It should be noted that

Next, in the period E, the voltage level (signal 301) of the gate signal line 213 is set to "L2", and the voltage level (signal 302) of the reset signal line 214 is set to "L2", The voltage level (signal 303) of the gate signal line 215 is set to " H ". As a result, transistor 208 is turned on and photosensor reference signal line 212 and photosensor output signal line 216 are conducted through transistors 205 and 208. Then, the voltage level (signals 305A to 305C) of the photosensor output signal line 216 is increased in accordance with the light incident on the photodiode 204. Note that in the period before the period E, the voltage level of the precharge signal line 218 is set to " H " so that the precharge of the photosensor output signal line 216 can be completed. Here, the speed at which the voltage level (signals 305A to 305C) of the photosensor output signal line 216 increases is the current between the source and the drain of the transistor 205, i.e., incident to the photodiode 204 during period C, which is an accumulation operation period. It increases with the amount of light. As described above, the period E is a selection operation period.

Next, in the period F, the voltage level (signal 301) of the gate signal line 213 is set to "L2", and the voltage level (signal 302) of the reset signal line 214 is set to "L2", The voltage level (signal 303) of the gate signal line 215 is set to "L". As a result, the transistor 208 is turned off, and the voltage level (signals 305A to 305C) of the photosensor output signal line 216 is constant. Here, the constant value is determined according to the amount of light incident on the photodiode 204. Thus, the amount of light incident on the photodiode 204 during the accumulation operation can be determined by obtaining the voltage level of the photosensor output signal line 216. As described above, the period F is a read operation period.

As described above, in the semiconductor device of the present embodiment, the voltage level of the voltage applied to the gate of the transistor 206 and the voltage level of the voltage applied to the gate of the transistor 207 are while the transistor 206 is off. The periods D, E, and F, and the periods A, D, E, and F while the transistor 207 is off are set lower than 0V. That is, the voltage level of the voltage applied between the gate and the source of the transistor 206 is set below the level of the threshold voltage of the transistor 206, and the voltage of the voltage applied between the gate and the source of the transistor 207. The level is set below the level of the threshold voltage of the transistor 207. Therefore, the function of retaining the charge held in the gate of the transistor 205 can be improved.

More specifically, the operation of the individual photosensor is realized by repeatedly performing the reset operation, the accumulation operation, the selection operation and the read operation. As described above, in the present embodiment, the voltage level of the voltage applied to the gate of the transistor 206 and the voltage level of the voltage applied to the gate of the transistor 207 are measured while the transistors 206 and 207 are turned off. In the period is lower than 0 V. Thus, the transistors 206 and 207 can be turned off more reliably, thereby improving the function of retaining the charge held at the gate of the transistor 205 during the accumulation operation and the read operation. In addition, the function of accurately converting incident light into an electrical signal of the photosensor can be improved. In addition, it is preferable that the semiconductor layer of the transistor 206 and the semiconductor layer of the transistor 207 use transistors to obtain transistors having a very low off current. By this structure, the function of converting the incident light into the electrical signal of the photosensor more accurately can be improved.

This embodiment can be combined with any other embodiment as appropriate.

(Embodiment 2)

In this embodiment, a method of driving a plurality of photosensors will be described.

First, the driving method is described in the timing chart of FIG. In Fig. 4, signals 401, 402 and 403 are signals showing the voltage change of the reset signal line 214 in the photosensors of the first row, second row and third row, respectively. Signals 404, 405, and 406 are signals showing the voltage change of the gate signal line 213 in the photosensors of the first row, second row, and third row, respectively. Signals 407, 408, and 409 are signals showing the voltage change of the gate signal line 215 in the photosensors of the first row, second row, and third row, respectively. The period 410 is a period required for one imaging. The period 411 is a period during which the reset operation is performed in the photosensors in the second row, the period 412 is a period during the accumulation operation is performed in the photosensors in the second row, and the period 413 is the period during This is the period during which the selection operation is performed on the photosensors in two rows. Thus, an image can be obtained by driving the photosensors in each row in turn.

Here, it can be seen that there is a time delay in the accumulation operation in the photosensors in each row. That is, the imaging by the photosensors in each row is not performed simultaneously, resulting in a distortion phenomenon in which the image is blurred. In particular, an image of a rapidly moving object to be detected is easily obtained in a distorted shape: when the object is moved in the direction of the first to third rows, an enlarged image is obtained leaving a trailing trail behind; When the object to be detected moves in the opposite direction, a reduced image is obtained.

In order to prevent the time delay of the accumulation operation in the photosensors in each row, it is effective that the photosensors in each row are sequentially driven at short periods. In this case, however, the output signal of the photosensor must be obtained at a very high speed in the OP amplifier or A / D conversion circuit, which leads to an increase in power consumption, and in particular, it is very difficult to obtain a high resolution image.

Therefore, the driving method shown in the timing chart of FIG. 5 is proposed. In Fig. 5, signals 501, 502 and 503 are signals showing the voltage change of the reset signal line 214 of the photosensors of the first row, the second row and the third row, respectively. Signals 504, 505 and 506 are signals showing the voltage change of the gate signal line 213 of the photosensors of the first row, the second row and the third row, respectively. Signals 507, 508 and 509 are signals showing the voltage change of the gate signal line 215 of the photosensors of the first row, second row and third row, respectively. The period 510 is a period required for one imaging. The period 511 is a period during which the reset operation (in all rows) is performed in the photosensors in the second row, and the period 512 is the accumulation operation (in all rows simultaneously) in the photosensors in the second row. Is a period during which the selection operation is performed (in all rows at the same time) in the photosensors of the second row.

FIG. 5 differs from FIG. 4 in that the reset operation and the accumulation operation are each performed in the same period in the photosensors of all the rows, and the selection operation after the accumulation operation is sequentially performed in each row without synchronization with the accumulation operation. When the accumulation operation is performed in the same period, the image of the object to be detected can be easily obtained without blur even when imaging at the photosensors in each row is performed simultaneously and the object moves rapidly. Since the accumulation operation is performed at the same time, the driving circuit can be provided in common to the reset signal line 214 of each photosensor. In addition, the driving circuit may be provided in common to the gate signal line 213 of each photosensor. Such a drive circuit commonly provided is effective in reducing the number of peripheral circuits or reducing power consumption. In addition, the selection operation sequentially performed in each row may lower the operation speed of the OP amplifier or the A / D conversion circuit when the output signal of the photosensor is obtained. At this time, it is preferable that the total time for the selection operation is longer than the time for the accumulation operation, which is particularly effective in obtaining a high resolution image.

5 shows a timing chart of a method for sequentially driving each row of photosensors; Note that it is also effective to sequentially drive the photosensors only in certain rows to obtain images in certain areas. As a result, a desired image can be obtained while the operation and power consumption of the OP amplifier or A / D conversion circuit are reduced. Also, a driving method for driving some of the photosensors every few rows, that is, a plurality of photosensors, is also effective. As a result, it is possible to obtain an image having a required resolution while reducing the operation of an op amp or an A / D conversion circuit and reducing power consumption.

In order to realize the above driving method, the voltage level of the gate of the transistor 205 in each photosensor must be kept constant even after the accumulation operation is completed. Thus, as described in the above embodiment, the transistor 207 preferably uses an oxide semiconductor to make the off current very small.

In this manner, it is possible to provide a low power consumption display device or a semiconductor device that enables a high-resolution to-be-detected image with almost no blur distortion even when a target object moves at high speed.

This embodiment can be combined with any other embodiment as appropriate.

(Embodiment 3)

In this embodiment, a modification of the circuit configuration of the photosensor 106 in FIG. 2 will be described.

FIG. 6A shows a configuration in which the transistor 207 for controlling the reset operation of the photosensor, which is connected to the gate of the transistor 205 in FIG. 2, is omitted. In the configuration of FIG. 6A, when the reset operation of the photosensor is performed, the charge accumulated in the gate of the transistor 205 can be discharged by changing the voltage level of the wiring 211.

6B shows a configuration in which the transistors 205 and 208 are connected in the opposite manner as in the photosensor 106 of FIG. 2. In particular, one of the source and the drain of the transistor 205 is connected to the photosensor output signal line 216, and one of the source and the drain of the transistor 208 is connected to the photosensor reference signal line 212.

FIG. 6C shows a configuration in which the transistor 208 is omitted from the configuration of the photosensor 106 of FIG. 2. The configuration of Fig. 6C is different from that of Figs. 2, 6A, and 6B: When the selection operation and the read operation of the photosensor are performed, the change in the signal corresponding to the charge accumulated in the gate of the transistor 205 is changed. It can be read by changing the voltage level of the sensor reference signal line 212.

A timing chart relating to the operation of the photosensor 106 shown in FIG. 6C is shown in FIG. In FIG. 10, the signals 601, 602, and 603 correspond to voltage levels of the gate signal line 213, the reset signal line 214, and the photosensor reference signal line 212 in FIG. 6C, respectively. The signal 604 corresponds to the voltage level of the gate of the transistor 205 and shows the case where the illuminance of the light incident on the photodiode 204 is medium (hereinafter, medium illuminance). Signal 605 shows the voltage level of photosensor output signal line 216. Signal 606 shows the voltage level of node 611 in FIG. 6C.

The timing chart of FIG. 10 is described. In the period A, the levels of the signal 601 and the signal 603 are set to "H", and the voltage level of the signal 602 is set to "L2". Then, in period B, if the voltage level of the signal 602 is set to "H", the voltage level of the signal 604 is reset, and the voltage levels of the signals 605 and 606 increase. That is, the periods A and B are reset operation periods. Next, in the period C, if the voltage level of the signal 601 is set to "L2", the voltage level of the signal 606 decreases. Then, in the period D, the voltage levels of the signals 602 and 603 are set to "L2". That is, the period C and the period D are accumulation operation periods. Next, in the period E, when the voltage levels of the signal 601 and the signal 603 are set to "H", the voltage level of the signal 604 and the voltage level of the signal 606 become the same voltage level, and the photosensor The voltage level of the signal 605 changes in accordance with the output signal. That is, the period E is a selection operation period. Then, in the period F, the voltage levels of the signal 601 and the signal 603 are set to "L2", and the voltage level of the signal 605 is read. That is, the period F is a read operation period. In this way, the operation of the photosensor 106 shown in FIG. 6C can be performed.

This embodiment can be combined with any other embodiment as appropriate.

(Fourth Embodiment)

In this embodiment, the structure and manufacturing method of the semiconductor device including the photosensor will be described. 7 is a cross-sectional view of a semiconductor device. It should be noted that the following semiconductor device can be applied to a display device.

In FIG. 7, photodiode 1002, transistor 1003, and transistor 1004 are provided over substrate 1001 having an insulating surface. Each of the photodiode 1002, transistor 1003, and transistor 1004 is a cross sectional view of the photodiode 204, transistor 205, and transistor 206 in FIG. 2. Light 1202 emitted from the detected object 1201, external light 1202 reflected by the detected object 1201, or light 1202 emitted inside the apparatus and reflected by the detected object 1201 ) Is incident on the photodiode 1002. The detected object may be provided on the substrate 1001 side.

The substrate 1001 is an insulating substrate (for example, a glass substrate or a plastic substrate), an insulating substrate having an insulating film (for example, a silicon oxide film or a silicon nitride film) formed thereon, or a semiconductor having an insulating film formed thereon. It may be a substrate (eg, a silicon substrate) or a metal substrate (eg, an aluminum substrate) on which an insulating film is formed.

The photodiode 1002 is a lateral-junction pin diode and includes a semiconductor film 1005. The semiconductor film 1005 includes a p-type conductive region (p-layer 1021), an i-type conductive region (i-layer 1022) and an n-type conductive region (n-layer 1023). It includes. It should be noted that the photodiode 1002 may be a pn diode.

The horizontal junction pin or the pn diode may be formed by adding p-type impurities and n-type impurities to a specific region of the semiconductor film 1005.

In the photodiode 1002, in order to improve the ratio (quantum efficiency) of the electrical signal generated from the incident light, it is preferable that a single crystal semiconductor (for example, single crystal silicon) having few crystal defects is used for the semiconductor film 1005. Do.

The transistor 1003 is a top-gate thin film transistor and includes a semiconductor film 1006, a gate insulating film 1007, and a gate electrode 1008.

The transistor 1003 has a function of converting the electric charge supplied from the photodiode 1002 into an output signal. Therefore, a single crystal semiconductor (for example, single crystal silicon) is preferably used for the semiconductor film 1006 to obtain a transistor with high mobility.

An example of forming the semiconductor film 1005 and the semiconductor film 1006 using a single crystal semiconductor will be described. The damaged region is formed at a desired depth of the single crystal semiconductor substrate (eg, single crystal silicon substrate) using ion irradiation or the like. The single crystal semiconductor substrate and the substrate 1001 are adhered to each other with an insulating film sandwiched therebetween, and the single crystal semiconductor substrate is then separated along the damaged region, so that a semiconductor film is formed on the substrate 1001. The semiconductor film is processed (patterned) into a desired form by etching or the like so that the semiconductor film 1005 and the semiconductor film 1006 are formed. Since the semiconductor film 1005 and the semiconductor film 1006 can be formed in the same process, cost reduction can be realized. In this way, the photodiode 1002 and the transistor 1003 can be formed on the same surface.

It should be noted that amorphous semiconductors, microcrystalline semiconductors, polycrystalline semiconductors, oxide semiconductors, and the like may be used for the semiconductor film 1005 and the semiconductor film 1006. In particular, single crystal semiconductors are preferably used to obtain transistors with high mobility. As the semiconductor material, it is preferable to use a silicon semiconductor such as silicon or silicon germanium which can easily improve crystallinity.

Here, the semiconductor film 1005 is preferably made thick to improve the quantum efficiency of the photodiode 1002. In addition, the semiconductor film 1006 is preferably made thin in order to improve electrical characteristics such as the S value of the transistor 1003. In this case, what is required only in the semiconductor film 1005 is to be made thicker than the semiconductor film 1006.

Crystalline semiconductors are preferably used in transistor 208 of FIG. 2 to obtain transistors with high mobility. By using the same semiconductor material as the transistor 1003, the cost is saved because the transistor 208 can be formed in the same process as the transistor 1003.

It should be noted that the gate insulating film 1007 is formed in a single layer or a lamination using a silicon oxide film, a silicon nitride film, or the like. The gate insulating film 1007 may be formed by plasma CVD or sputtering.

It should be noted that the gate electrode 1008 is formed in a single layer or lamination using a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium or scandium, or an alloy material based on such material. Gate electrode 1008 may be formed by sputtering or vacuum deposition.

The photodiode 1002 may have a stacked structure of p-layers, i-layers, and n-layers instead of lateral junction structures. The transistor 1003 may be a bottom-gate transistor, and may have a channel-stop structure or a channel-etched structure.

As shown in FIG. 9, it should be noted that the light shielding film 1301 may be provided under the photodiode 1002 so that light other than the light to be sensed may be blocked. The light shielding film may be provided over the photodiode 1002. In this case, the light shielding film may be provided, for example, on the substrate 1302 opposed to the substrate 1001 on which the photodiode 1002 is provided.

The transistor 1004 is a thin film transistor having a bottom-gate inverted-staggered structure, and includes a gate electrode 1010, a gate insulating film 1011, a semiconductor film 1012, an electrode 1013, and an electrode. 1014. An insulating film 1015 is provided over the transistor 1004. Note that transistor 1004 may be a top-gate transistor.

The feature of this structure is that the transistor 1004 is formed over the photodiode 1002 and the transistor 1003 with an insulating film 1009 interposed therebetween. If transistor 1004 and photodiode 1002 are formed over other layers in this manner, the area of photodiode 1002 may increase, increasing the amount of light received by photodiode 1002.

Further, part or all of the transistor 1004 is preferably formed so as to overlap with either the n-layer 1023 or the p-layer 1021 of the photodiode 1002. This is because the area of the photodiode 1002 can be increased and the overlapping area of the transistor 1004 and the i-layer 1022 can be made as small as possible to efficiently receive light. Also in the case of a pn diode, light reception is made more efficient by making the overlap region of the transistor 1004 and the pn junction smaller.

The function of the transistor 1004 is to accumulate the output signal of the photodiode 1002 as a charge in the gate of the transistor 1003 and hold this charge. Therefore, it is preferable that an oxide semiconductor be used for the semiconductor film 1012 so that the transistor has a very low off current.

In addition, the transistor 207 of FIG. 2 preferably uses an oxide semiconductor to have a very low off current. By using the same semiconductor material as the transistor 1004, the transistor 207 can be formed in the same process as the transistor 1004, thereby reducing the cost. Note that for each of the above semiconductor elements, a thin film semiconductor or a bulk semiconductor can be used.

An example of forming the semiconductor film 1012 using an oxide semiconductor is shown below.

One of the factors that increase the off current of the transistor is an impurity such as hydrogen (eg, hydrogen, water, or hydroxyl) included in the oxide semiconductor. Hydrogen or the like may be a carrier supply (donor) in the oxide semiconductor, which becomes a factor for generating current even in the off state. That is, the oxide semiconductor containing a large amount of hydrogen or the like becomes an n-type oxide semiconductor.

Therefore, in the manufacturing method shown below, the amount of hydrogen in the oxide semiconductor is reduced as much as possible, and the concentration of oxygen as a constituent element is increased, so that the oxide semiconductor has high purity. High purity oxide semiconductors are intrinsically or substantially intrinsic semiconductors, thus reducing off current.

First, an oxide semiconductor film is formed on the insulating film 1009 by sputtering.

As the target used to form the oxide semiconductor film, a target of a metal oxide containing zinc oxide as a main component can be used. For example, as a composition ratio, it is possible to use a target having In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1, that is, In: Ga: Zn = 1: 1: 0.5. In addition, a target having a composition ratio of In: Ga: Zn = 1: 1: 1 or a composition ratio of In: Ga: Zn = 1: 1: 2 can be used. It is also possible to use a target comprising SiO ₂ of ₂ % by weight or more and 10% by weight or less.

It should be noted that the oxide semiconductor film can be formed in a rare gas (generally argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of the rare gas and oxygen. Here, the sputtering gas used to form the oxide semiconductor film is a high purity gas whose concentration of impurities such as hydrogen, water, hydroxyl or hydride is reduced to a level such that ppm, preferably ppb, can be expressed.

The oxide semiconductor film is formed by introducing a sputtering gas from which hydrogen and moisture have been removed while removing moisture remaining in the processing chamber. In order to remove the water remaining in the processing chamber, an entrapment vacuum pump is preferably used. For example, cryopumps, ion pumps, or titanium sublimation pumps are preferably used.

The oxide semiconductor film may have a thickness of 2 nm or more and 200 nm or less, preferably 5 nm or more and 30 nm or less. Then, the oxide semiconductor film is processed (patterned) into a desired shape by the etching or the like to form a semiconductor film 1012.

In-Ga-Zn-O is used for the oxide semiconductor film in the above examples, but the following oxide semiconductors can also be used: In-Sn-Ga-Zn-O, In-Sn-Zn-O, In-Al-Zn -O, Sn-Ga-Zn-O, Al-Ga-Zn-O, Sn-Al-Zn-O, In-Zn-O, Sn-Zn-O, Al-Zn-O, Zn-Mg-O , Sn-Mg-O, In-Mg-O, In-O, Sn-O, Zn-O and the like. The oxide semiconductor film may include Si. In addition, the oxide semiconductor film may be amorphous or crystalline. In addition, the oxide semiconductor film may be a non-single crystal or a single crystal.

As the oxide semiconductor film, a thin film expressed by InM0 ₃ (ZnO) m (m> 0) can also be used. Here, M represents at least one metallic material selected from Ga, Al, Mn and Co. For example, M may be Ga, Ga and Al, Ga and Mn, or Ga and Co.

Next, the first heat treatment is performed on the oxide semiconductor film (semiconductor film 1012). The temperature of the first heat treatment is 400 ° C or more and 750 ° C or less, preferably 400 ° C or more and less than the distortion point of the substrate.

Through the first heat treatment, hydrogen, water, hydroxyl groups and the like can be removed (dehydrogenation treatment) from the oxide semiconductor film (semiconductor film 1012). Since such impurities become donors in the oxide semiconductor film to increase the off current of the transistor, the dehydrogenation treatment through the first heat treatment is quite effective.

The first heat treatment may be performed using an electric furnace. Also, heat conduction or thermal radiation from a heating element such as a resistive heating element can be used for the first heat treatment. In that case, a rapid thermal annealing (RTA) apparatus such as a gas rapid thermal annealing (GRTA) apparatus or a lamp rapid thermal annealing (LRTA) apparatus may be used.

The LRTA apparatus is for heating a workpiece to be treated by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp or a high pressure mercury lamp. Device.

GRTA device is a device for heat treatment using hot gas. As the gas, an inert gas (generally, a rare gas such as argon) or nitrogen gas can be used. The use of GRTA devices is particularly effective because of the high temperature heat treatment in a short time.

The first heat treatment may be performed before patterning the oxide semiconductor film, after formation of the electrode 1013 and the electrode 1014, or after formation of the insulating film 1015. However, the first heat treatment is preferably performed before the formation of the electrode 1013 and the electrode 1014 so that the electrode is not damaged by the first heat treatment.

During the first heat treatment, oxygen deficiency may occur in the oxide semiconductor. Therefore, after the first heat treatment, oxygen is preferably introduced into the oxide semiconductor (a treatment for supplying oxygen), and the oxide semiconductor is made highly purified by increasing the concentration of oxygen as a constituent element.

In particular, as a treatment for supplying oxygen, after the first heat treatment, the second heat treatment may be, for example, in an oxygen atmosphere or an atmosphere containing nitrogen and / or oxygen (eg, nitrogen: oxygen ratio is 4: 1). Followed by Further, the plasma treatment can be performed in an oxygen atmosphere, whereby the oxygen concentration of the oxide semiconductor film can be increased and the oxide semiconductor film can be made highly purified. The temperature of 2nd heat processing is 200 degreeC or more and 400 degrees C or less, Preferably it is 250 degreeC or more and 350 degrees C or less.

As another example of the processing for supplying oxygen, an oxide insulating film (insulating film 1015) is formed in contact on the semiconductor film 1012 and then a third heat treatment is performed. Oxygen in the insulating film 1015 may move to the semiconductor film 1012 so as to increase the oxygen concentration in the oxide semiconductor, and the oxide semiconductor film may be highly purified. The temperature of 3rd heat processing is 200 degreeC or more and 400 degrees C or less, Preferably they are 250 degreeC or more and 350 degrees C or less. Further, in the case of the top-gate transistor, it should be noted that the oxide semiconductor can be highly purified in such a manner that a gate insulating film in contact with the semiconductor film 1012 is formed of a silicon oxide film or the like and similar heat treatment is performed.

As described above, the oxide semiconductor film may be highly purified through an oxygen supply treatment such as a second heat treatment or a third heat treatment after the dehydrogenation treatment by the first heat treatment. Once highly purified, the oxide semiconductor can be intrinsic or substantially intrinsic, reducing the off current of transistor 1004.

It is to be noted that the insulating film 1009 is formed over the photodiode 1002 and the transistor 1003 in a single layer or stacked structure using a silicon oxide film, a silicon nitride film, or the like. The insulating film 1009 may be formed by plasma CVD or sputtering. The insulating film 1009 may also be formed of a resin film such as a polyimide film by coating or the like.

The gate electrode 1010 formed over the insulating film 1009 uses a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium, or an alloy material containing predetermined materials as main components. Thereby forming a single layer or a laminated structure. The gate electrode 1010 may be formed by sputtering or vacuum deposition.

The gate insulating film 1011 is formed in a single layer or a laminated structure using a silicon oxide film, a silicon nitride film, or the like. The gate insulating film 1011 may be formed by plasma CVD or sputtering.

Each of the electrode 1013 and the electrode 1014 formed on the gate insulating film 1011 and the semiconductor film 1012 includes a metal such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, yttrium, or predetermined materials thereof. It is formed in a single layer or a laminated structure using an alloying material or a metal oxide having conductivity such as indium oxide. The electrode 1013 and the electrode 1014 may be formed using sputtering or vacuum deposition. Here, the electrode 1013 is preferably connected to the n-layer 1023 of the photodiode 1002 through contact holes formed in the gate insulating film 1007, the insulating film 1009, and the gate insulating film 1011.

Next, a highly purified oxide semiconductor and a transistor using the same will be described in detail.

As an example of a highly purified oxide semiconductor, the carrier concentration is less than 1 × 10 ¹⁴ / cm ³ , preferably less than 1 × 10 ¹² / cm ³ , more preferably less than 1 × 10 ¹¹ / cm ³ or 6.0 × 10 ¹⁰ / and oxide semiconductors of less than cm ³ .

Transistors using highly purified oxide semiconductors are characterized by a much lower off current than, for example, transistors including silicon-containing semiconductors.

The following shows the measurement results of the off-current characteristics of the transistors using an evaluation device (also called a test element group (TEG)). Note that an n-channel transistor is described here.

The TEG is provided with a transistor of L / W = 3 µm / 10000 µm, which is produced by connecting 200 transistors of L / W = 3 µm / 50 µm (thickness d: 30 nm) in parallel. 8 shows the initial characteristics of the transistor. Here, VG exists in the range of -20V or more and + 5V or less. To measure the initial characteristics of the transistor, the substrate temperature is set to room temperature, the voltage between the source and drain (hereinafter also referred to as drain voltage or VD) is set to 1 V or 10 V, and the voltage between the source and gate (hereinafter, The change characteristics of the source-drain current (hereinafter also referred to as drain current or ID), that is, the VG-ID characteristic, were measured under conditions in which the gate voltage or VG was changed from -20 V to +20 V.

As shown in FIG. 8, a transistor having a channel width W of 10000 μm has an off current of 1 × 10 ⁻¹³ A or less at VD of 1 V and 10 V, which is a measuring device (Semiconductor Parameter Analyzer, Agilent, manufactured by Agilent Corporation). 4156C) or less (100 fA). The off current value per channel width of 1 μm corresponds to 10 aA / μm.

In addition, in the present specification, the off current (also referred to as leakage current) is used in the n-channel transistor when the gate voltage selected from the range of -20 V or more and -5 V or less at room temperature is applied when the threshold value V _th is positive. Note that the current flowing between the source and the drain of the n-channel transistor. In addition, it should be noted that room temperature is 15 degreeC or more and 25 degrees C or less. Transistors comprising oxide semiconductors described herein have a current value per unit channel width (W) of 100 aA / μm or less, preferably 1 aA / μm or less, more preferably 10 zA / μm or less at room temperature.

In addition, a transistor including a high purity oxide semiconductor has good temperature characteristics. Typically, in the temperature range from -25 ° C to 150 ° C, the transistor's current voltage characteristics such as on-current, off current, field effect mobility, S-value, and threshold voltage are almost unchanged and the current voltage due to temperature Deterioration of the characteristics is hardly seen.

This embodiment can be combined with any of the other embodiments as appropriate.

This application is based on Japanese Patent Application No. 2010-050776 for which it applied to Japan Patent Office on March 8, 2010, The whole content is integrated in this specification by reference.

100: display panel
101: pixel circuit
102: display element control circuit
103: photosensor control circuit
104: pixels
105: display element
106: photosensor
107: display element driving circuit
108: display element driving circuit
109: photosensor reading circuit
110: photosensor driving circuit
200: precharge circuit
201: transistor
202: storage capacitor
203: liquid crystal element
204 photodiode
205 transistor
206: transistor
207 transistors
208: transistor
209: gate signal line
210: video data signal line
211: wiring
212: photo sensor reference signal line
213: gate signal line
214: reset signal line
215: gate signal line
216: photo sensor output signal line
217: Transistor
218: precharge signal line
219: node
301 to 305: signal
401 to 409: signal
410-413: period
501 to 509: signal
510 to 513: period
601 to 606: signal
611: node
1001: substrate
1002: photodiode
1003: transistor
1004: transistor
1005: semiconductor film
1006: semiconductor film
1007: gate insulating film
1008: gate electrode
1009: insulating film
1010: gate electrode
1011: gate insulating film
1012: semiconductor film
1013: electrode
1014: electrode
1015: insulating film
1021: p-layer
1022: i-layer
1023: n-layer
1201: detectable
1202: light
1301: light shielding film
1302: substrate

Claims (22)

A semiconductor device comprising:
Photodiode;
A first transistor;
A second transistor;
A third transistor; And
Including a fourth transistor,
A first terminal of the photodiode is electrically connected to a first terminal of the second transistor,
A second terminal of the second transistor is electrically connected to a gate of the first transistor and a first terminal of the third transistor,
A first terminal of the first transistor is electrically connected to a first terminal of the fourth transistor,
In the first period, charges corresponding to the amount of incident light to the photodiode are accumulated in the gate of the first transistor,
In a second period, the charge is retained in the gate of the first transistor while a first voltage is applied to the gate of the second transistor and a second voltage is applied to the gate of the third transistor,
The voltage level of the first voltage is lower than the voltage level of the first terminal of the second transistor and the voltage level of the second terminal of the second transistor, and the voltage level of the second voltage is the first terminal of the third transistor. And a voltage level lower than a voltage level of the second terminal of the third transistor. The method of claim 1,
And the semiconductor layer of the second transistor comprises an oxide semiconductor. The method of claim 1,
A semiconductor device, wherein the semiconductor layer of the third transistor contains an oxide semiconductor. The method of claim 1,
And the semiconductor layer of the second transistor and the semiconductor layer of the third transistor include an oxide semiconductor. The method of claim 1,
And the voltage level of the first voltage is lower than the voltage level of the second terminal of the photodiode. The method of claim 1,
Wherein the charge is discharged from the gate of the first transistor while a third voltage is applied to the gate of the third transistor and a fourth voltage is applied to the second terminal of the third transistor. The method of claim 1,
Wherein the charge is discharged from the gate of the first transistor while a fifth voltage is applied to the second terminal of the photodiode and a sixth voltage is applied to the gate of the second transistor. A semiconductor device comprising:
Photodiode;
A first transistor;
A second transistor; And
A third transistor,
A first terminal of the photodiode is electrically connected to a first terminal of the second transistor,
A second terminal of the second transistor is electrically connected to a gate of the first transistor and a first terminal of the third transistor,
In the first period, charges corresponding to the amount of incident light to the photodiode are accumulated in the gate of the first transistor,
In a second period, the charge is retained in the gate of the first transistor while a first voltage is applied to the gate of the second transistor and a second voltage is applied to the gate of the third transistor,
The voltage level of the first voltage is lower than the voltage level of the first terminal of the second transistor and the voltage level of the second terminal of the second transistor, and the voltage level of the second voltage is the first terminal of the third transistor. And a voltage level lower than a voltage level of the second terminal of the third transistor. 9. The method of claim 8,
And the semiconductor layer of the second transistor comprises an oxide semiconductor. 9. The method of claim 8,
A semiconductor device, wherein the semiconductor layer of the third transistor contains an oxide semiconductor. 9. The method of claim 8,
And the semiconductor layer of the second transistor and the semiconductor layer of the third transistor include an oxide semiconductor. 9. The method of claim 8,
And the voltage level of the first voltage is lower than the voltage level of the second terminal of the photodiode. 9. The method of claim 8,
Wherein the charge is discharged from the gate of the first transistor while a third voltage is applied to the gate of the third transistor and a fourth voltage is applied to the second terminal of the third transistor. 9. The method of claim 8,
Wherein the charge is discharged from the gate of the first transistor while a fifth voltage is applied to the second terminal of the photodiode and a sixth voltage is applied to the gate of the second transistor. A semiconductor device comprising:
Photodiode;
A first transistor; And
A second transistor,
A first terminal of the photodiode is electrically connected to a first terminal of the second transistor,
A second terminal of the second transistor is electrically connected to a gate of the first transistor,
In the first period, charges corresponding to the amount of incident light to the photodiode are accumulated in the gate of the first transistor,
In a second period, the charge is retained in the gate of the first transistor while a first voltage is applied to the gate of the second transistor,
And the voltage level of the first voltage is lower than the voltage level of the first terminal of the second transistor and the voltage level of the second terminal of the second transistor. 16. The method of claim 15,
And the semiconductor layer of the second transistor comprises an oxide semiconductor. 16. The method of claim 15,
And the voltage level of the first voltage is lower than the voltage level of the second terminal of the photodiode. 16. The method of claim 15,
Wherein the charge is discharged from the gate of the first transistor while a fifth voltage is applied to the second terminal of the photodiode and a sixth voltage is applied to the gate of the second transistor. As a driving method of a semiconductor device,
The charge is accumulated in the gate of the first transistor by applying a first voltage to the first terminal of the photodiode, applying a second voltage to the gate of the second transistor, and applying a third voltage to the gate of the third transistor. Making;
Maintaining the charge in the gate of the first transistor by applying a fourth voltage to the gate of the second transistor and applying a fifth voltage to the gate of the third transistor; And
Discharging the charge from the gate of the first transistor by applying a sixth voltage to the gate of the third transistor and applying a seventh voltage to the first terminal of the third transistor,
The charge corresponds to the amount of incident light to the photodiode,
In the step of holding the charge, the voltage level of the fourth voltage is lower than the voltage level of the first terminal of the second transistor and the voltage level of the second terminal of the second transistor, and the voltage level of the fifth voltage is And a voltage level of the first terminal of the third transistor and a voltage level of the second terminal of the third transistor. 20. The method of claim 19,
And the voltage level of the third voltage is equal to the voltage level of the fifth voltage. As a driving method of a semiconductor device,
Accumulating charge in the gate of the first transistor by applying a first voltage to the first terminal of the photodiode and applying a second voltage to the gate of the second transistor;
Maintaining the charge in the gate of the first transistor by applying a third voltage to the gate of the second transistor; And
Discharging the charge from the gate of the first transistor by applying a fourth voltage to the gate of the second transistor and applying a fifth voltage to the first terminal of the photodiode,
The charge corresponds to the amount of incident light to the photodiode,
In the step of holding the charge, the voltage level of the third voltage is lower than the voltage level of the first terminal of the second transistor and the voltage level of the second terminal of the second transistor. The method of claim 21,
And the voltage level of the second voltage is equal to the voltage level of the fourth voltage.

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